Average latency without histograms

[baryluk]

Is there a way to enable grpc_server_handling_seconds_sum and grpc_server_handling_seconds_count, so one can do aggregations and computations of average latency:

grpc_server_handling_seconds_sum{grpc_code="OK",grpc_method="PingList",grpc_service="mwitkow.testproto.TestService",grpc_type="server_stream"} 0.0003866430000000001
grpc_server_handling_seconds_count{grpc_code="OK",grpc_method="PingList",grpc_service="mwitkow.testproto.TestService",grpc_type="server_stream"} 1
...

without the full blown histograms (which do have storage cost on Prometheus)?

Even better, would be ability to have also metrics without grpc_code, but I believe this is tracked in a separate issue.

PS. Also for client calls the same.